Method and apparatus for determining the location of producing horizons in wells



Dec. 30, 1947. I TEPUTZ 2,433,718

' METHOD AND APPARATUS FOR DETERMINING THE LOCATION OF PRODUCINGHORIZONS IN WELLS Filed April 10, 1945 2 Sheets-Sheet l Mn *Mlzy/ 1 A? IW I v v a I z s a IIIIIIIIIIIIIIIIIlllllllllllllllllllllllll'lllll Dec.30, 1947. n-z 2,433,718

METHOD AND APPARATUS FOR DETERMINING THE LOCATION OF PRODUCING HORIZONSIN WELLS Filed April 10, 1.945 2 Sheets-$heet 2 E EJMW i-"SBRf-XHJKM aTEPLITZ r Y fg. 6. 32

Patented Dec. 30, 1947 METHOD .AND. APPARATUS FOR' DETER- MINING THELOCATI ON-OF PRODUCING HORIZONS IN WELLS- Abraham J. .Teplitz, Oakmont;Pa.,- assignor .to

:Gulf Research &;Development Compa ny,'Pittsburgh; Pa., a corporation ofDelaware Application April '10, 1945'. Serial No.- 587,532

8 Claims. (01. 250--83) This invention pertains to a-methodbfandapparatus for determining the position-ofwater pr oil producing horizonsin a well'by radiological means.

In the production of oil from wells, it is customary proceduretosetcasing in-the well' and-.to place oppositethe producing formationascreen or strainer through which fluid may pass into the casing or thetubing string 'Such-a-screen allows the formation fluids to passinto-the well but tends to restrain sand or other solid matter fromdoing so. If sufficient formation'pressure exists, the well fluids willflow through the screen and up the producing tubing to the-surface. Ifinsufiicient formation pressure is available, a pump is usuallyinstalled in the tubing aboveithe screen.

Many oil producing formations do not' solely produce oil. The producingformation often is made up of a series of horizons, some of which areoil bearing and some of which are water bearing. If a screen is setopposite the; entire length of producing formation, a mixture of oil andwater may be produced-and, moreover, this mixture may become emulsifiedso that separation is difficult. Moreover, the water is usually salineand highly corrosive, and in a pumping well represents an expensive anduseless load. It is therefore important to determine the source horizonsof the water andoil .so that steps maybe taken to shut off or seal thewater producing. horizons and produce only oil.

The incursion of water into oil wellsrepresents one of the major sourcesof expense in the production of petroleum. The pumping of water,handling of emulsions, disposal of the .water, and the corrosionresulting from the water, are, all costly factors attending theoperation of wells producingwater along with oil. Insome cases it hasbeen possible to shut off the flow of water from the producing formationby mechanical and chemical methods, but a large number of suchtreatments have proved unsuccessful principally because of the inabilityto ascertain which portion of the formation was yieldingthe water.

The object of this inventionis to provide a method of locating thesources of water entering a well from the producing zone, thus making itpossible to apply suitable tr atment in theparticular interval where itisneeded, with consequent opportunity for success in recoveringwater-free pipe line oil.

Another object of this invention'is toprovide a simple, apparatus for.locating the sources oftwater; or=oi1 entering a .well from theproducingzone.

A further object .of' this invention. is to;provide a method ofdetermining-the points of entry of water in a well in such a manner7thattreatment may beapplie d immediately without dismantling equipment inthewell.

The objects are accomplished .as set forth -.;in the followingspecification, which also includes anexampleof apparatus for carryingout the method -of.my invention. Referenceis made to the drawing inwhich:

Fig. llis a-section of the earth showing .onei -form of my apparatus inplace in a producing well;

Fig. v2.is arecord obtainedfroma radiological examination .of the well.screenemployed in my invention;

. Fig, 3-shows details. ofconstruction of a'well screen which may beemployed'in my invention;

Fig. 4;is a transverse sectionof awell screen which maybe employed inmy, invention;

,Fig. 5 is a section through a form of-wirewhich retains the activematerial usedlin, myinvention; and

Fig; 6 is" a section through another form of wire which'maybe used tohold active material.

In general, my inventionjconsists of'settingppposite the producingformation, a special'screen orstrainer' coated, with or" impregnatedwith a water-soluble radioactive substance or mixture. Afterallowing thewell to produce for a suff cient lengthgf time, the screen maybe'examined'either in 'place in the well-or upon beingbrought to thesurface. Examination is madeby-meansofairinstrument sensitivetoemanations from the radioactive substance; It is evidentthat the lowestradioactivity will be found at'the point'or points where themostradioactivematerial has been dissolved away.

In one way of employing my invention, a .well is completedby setting astrainer oppositethe producing-zone in the conventional manner. This isshowndiagrammatically. in 'Fig. 1 in. which is indicated a wellpenetrating earth formations l, 2, 3-, 4, 5, 6, I, 8 and 9. Formations.4, .5, 6', land 8 are in the producing zone, but some of' these eitherinitially or subsequently will produce water and somewill-produce oil. Acasing I 0' is cemented at H. Equipment at the top of the well is notindicated since this is conventional. At the lower end of the casing I0is suspended the strainer I4 with a conventional packer [5 which maybeeither an expansion'type or a permanent seal. Inside the casingandprojectinginto the strainer is suspended the production tubing-l3.The strainer I4 is provided-with the usual-openingsthrough-its wall andalong its length; these openings 'being indicated by numeral l1.strainer is further provided with grooves I 8 cut in the outer face ofthe solid portion, said grooves being filled with a mixture consistingof a radioactive substance dissolved or suspended in a cement or plasticmaterial which is soluble in water.

A simplified sketch showing the details of a strainer which may beemployed is shown in Figs. 3 and l. The pipe 23 containing perforations24 and provided with separators 25, is wrapped with wire of thecross-section shown in Fig. 6 by 21, this wire having spacing lugs 23which form the openings 3| which permit fluid to enter the inside of thestrainer while restraining the entrance of sand and other solidparticles. The upper part of the screen assembly is equipped withthreads 29 for attachment with a suitable packing device and to thelower portion is fastened the set-shoe 30 containing a back pressurevalve assembly which permits washing around the outside of strainerwhile preventing the entrance of formation cavings into the inside ofthe screen.

The radioactive material is contained in grooves 32 in the wirewrapping. Wire wrapping of suitable type is conveniently formed byrunning wire, which may be stainless steel or bronze, of thecross-section 26 shown in Fig. through rollers designed to produce thespacing lug 28 (Fig. 6) and at the same time press in the outer edgemaking the groove 32 of a dove-tail shape which provides betterretention for the radioactive material.

A suitable mixture for filling these grooves may be made by mixingplaster of Paris with about per cent of its weight of finely groundcarnotite and then adding suflicient water to make a pasty mass. Thismass can then be thoroughly spread over the surface of a screen havingwire of the cross-section indicated. After allowing sufiicient time forthe mixture to partially set, the opening at the bottom of the screenmay be plugged and water pressure applied to the inside at the upper endthus washing the excess plaster out of the screen openings 3| andleaving the grooves 32 full of the radioactive material. The set plasterof Paris has a slight solubility in water (about 0.1 gram in 100 ml.)and will gradually be removed in the well by water moving past it.

Another method of forming the screen could be accomplished byincorporating a radioactive substance in a plastic, such as thepolyvinyl alcohol resins which are manufactured with varying degrees ofsolubility in water depending upon the method of preparation. Such amixture having considerable flexibility could be filled into the groovein the wire before the latter is wrapped around the pipe.

A considerable variety of straining devices are known to those familiarwith oil-field practice but any of these may either be provided withrecesses for retaining the radioactive material or be coated withradioactive material incorporated in a suitable binder or cement. It isdesirable in some cases to incorporate a radioactive element into thescreen wire itself, in which case the wire could be made of a magnesiumalloy or other alloy having a slight solubility in water. Also insteadof plaster of Paris, or plastic material, low solubility salts such asmagnesium phosphate, lithium triphosphate, calomel, and thallium iodidemay be used by first fusing the salt and dispersing the carnotite orother radioactive substance in the molten mass.

If the annular space between the strainer and the well bore is large sothat there exists the possibility that some of the fluid entering thewell may pass vertically up or down the annulus before entering thestrainer, this condition may be remedied by afiixing barriers of metal,leather or other material to the outside of the strainer, causing thefluids to travel horizontally from the formation through the strainer.

After setting th strainer, the well is put on production in the usualmanner. Later, when the well begins to produce appreciable quantities ofwater along with the oil, any suitable detector of radioactivity islowered into the well. Such a detector, indicated by numeral it in Fig.1, may be a Geiger counter or ionization chamber commonly used in makinggamma ray well surveys. The instrument is suspended by cable l2, overwhich indications of the radioactivity are obtained electrically andrecorded in any known manner. Cable [2 may pass through a lubricator atthe top of tubing [3 so measurements may be made while the well isproducing. Known devices are used to determine the depth of unit It.Measurements of the radioactive intensity are made over the entirelength of the strainer, and the results of the examination arecustomarily obtained in the form of a graph, such as is indicated inFig. 2.

In Fig. 2, numeral [9 represents a chart or record as obtained by aconventional recording means such as is used for gamma ray well logging.Along one side a scale 20 shows the depth of the detecting instrumentIS. A curve 2| whose arbitrary zero line is indicated by dotted line 22shows the measured intensity of radioactivity produced by the materialin strainer grooves l8 (Fig. 1). The curve 2 I shows a high value wherethe radioactive material in the grooves has not been disturbed, whilethe points of lowest intensity will be found opposite the waterproducing zone or zones. As illustrated in Fig.2, the curve 2| showshigh radioactive intensity opposite formations 4 and 5, indicating thatthese are oil producing horizons, while opposite the formation 6 a lowvalue of radioactivity is observed, indicating that this formationproduced water which removed the radioactive material from the adjacentsection of the strainer. In some cases a formation may produce both oiland water. Thus opposite the top of formation 8, for example, the curveshows an intermediate intensity 23 thereby indicating only a partialremoval of the water-soluble radioactive material. This means that theupper part of this formation produces a relatively smaller amount ofwater. The gradual decrease in radioactive material observed on thescreen progressing toward the bottom of formation 8 indicates that thereis a gradual increase in the amount of waterproduced. Thus one maydetermine that formation 8 produces a small amount of water at its topand a large amount of water at the bottom.

Once the water sources have been located by the method of thisinvention, any known suitable steps may be taken to stop the flow ofwater. The water producing horizons may be cemented off, or selectiveplugging operations may be performed on horizons which are indicated asproducing mixtures of oil and water. One of the particular advantages ofthis process is that the water producing formation may be located and inmany cases treated without removing the strainer, an operation which isoften rather costly.

In the case of oil wells which are producing water, similar informationmay be obtained by lowering into the well opposite the producing haveaccumulated in the bottom of the well dur-= in; previous production, it.would be desirable to ,fdisplacethe fluid in. the well. with dry oiljust ..before. makinga test. a p

The method and apparatus of .my invention may alternatively bev used fordetecting the point.

of entry of oil into a well by using an oil-soluble" radioactivematerial on the strainer. For holding the radioactive material in thiscase a matrix -may beused-which has suitable solubility characteristicsin oil. Suitable oil soluble materialsv are naphthalene, anthracene,orelemental sul-" phur. The radioactive substance may also be embeddedin oil resistant rubber such as Neoprene andjDup rene which"areonlyslightly .soluble in oil.

My invention may be further used to detect both the points of entry ofwater and the points of entry of oil by means of a single strainer inone production test. This is done by filling alternate grooves I8 on thestrainer with watersoluble and with oil-soluble radioactive material,the radioactive materials being so chosen that their emanations aredistinctive in order that they may be distinguished by the instrumentl6. This may b done by using for one material a radioactive compoundwhich gives off relatively soft gamma rays, while for the other materiala radioactive compound which gives off hard gamma rays may be used.After the production test a gamma ray log is first run using an ordinaryionization chamber in unit l6, and then repeated with a shield aroundthe unit IS. The first curve then indicates the presence of bothmaterials and the second indicates presence of only the hard rayproducing material. By comparing these curves with the known initialdistribution of the radioactive materials one may easily deduce whereoil is produced and where water is produced. Obviously also whereneither of the two materials are removed the formation is either barrenor produces gas.

The radioactive matrix material chosen should have a solubilitydepending on the duration of the production test made while the screenor strainer is in the well. Furthermore, artificially radioactivatedmaterials may be used provided only that their lifetime be sufiicientlylong to permit of making the necessary production and inspection tests.

My invention may also be used when it is desired to locate highlypermeable horizons which by-pass or short circuit the input fluid usedin water flooding operations. Such horizons, sometimes called thiefsands are encountered in input wells and may be located by setting aspecial strainer similar to that shown in Fig. 1. Fluid, usually waterin this case, is pumped down the well and flows out through the strainerinto the producing formations. The water-soluble radioactive materialused in grooves I8 should for this purpose be only slightly soluble, sothat it is not completely removed by the water flowing out into theformation. The degree of removal of radioactive material may beascertained from the radioactive intensity observed on examinationawith..:.i.ns trument l 6.; as indicated on; curve 2 I :1Fig.2 ;;A;.sligh t decrease in observedcradioactive ;;intensity--; results from onlya slight removal of .-,material indicating thatthe. adjacentformationistaking onlya small flow of water, whilealarge decrease results from alarger'removal of zradioactive material indicating that: this formationis takingalarge flow ofwater. Any fthief formations'taking excessivewater may thenbe. plugged or sealed by known methods.

Other well known variations of the equipment .in the'well may be madewithoutafiecting my invention.- The casing I0,-Fig. 1, may for, exampleextend all the way to the-bottom of the. hole and may haveperforationsalong-its length oppo- ,sitethe-producing formations. -Asanother; ex-

ample the, strainer may be eliminated and the outsideofe the perforatedcasing may contain, the

radioactive material that indicates the nature: of the produced fluids...--While Ihave shown the radioactive. material .placed in externalgrooves on thestrainer; such material may ,be otherwise disposed ;on thestrainer. Theessential feature is that its;,position may be detected andthat it come in contact with the fluid being produced from the adjacentformation. The distribution of radioactive material is advantageouslymade uniform along the length of the strainer, but any knowndistribution may be used as well. If the operator suspects loss ofmaterial while running the strainer into the hole, an initial testwith'the gamma ray instrument may be made after the strainer is in placeand before production is begun.

Other radioactive materials may be substituted for those mentioned, e.g. inorganic or organic derivatives of radioactive elements mixed with asuitable binder may be employed as the indicating substance.

What I claim is:

1. A method of determining the source of fluid entering a well whichcomprises placing in the well opposite the producing formation a knownconfiguration of solid radioactive material removable by the producedfluid, allowing the well to produce for a period suiflcient to remove aportion of said radioactive material and subsequently determining thedistribution of radioactive material remaining in the Well. I

2. A method of determining the source of fluid entering or leaving awell which comprises placing in the well a known configuration of solidradioactive material removable by the fluid flow, permitting the wellfluid to flow for a suflicient time to remove a portion of saidradioactive material and subsequently measuring the distribution ofradioactive material remaining in the well.

3. A method of determining the source of fluid entering a well whichcomprises placing in the well opposite the producing formation a knownconfiguration of solid radioactive material removable by the producedfluid, allowing the well to produce for a period sufficient to remove aportion of said radioactive material and examining the well with aninstrument sensitive to emanations from the radioactive material todetermine the regions in which said radioactive material has beenremoved by the fluid.

4. An apparatus for determining the source of any fluid being producedin a well comprising a strainer having associated therewith a knowndistribution of radioactive material soluble in said fluid, means forproducing the well and means for examining the strainer for radioactiveemanations to determine the regions in which said ra- 7 dioactivematerial has been removed by the fluid. 5. An apparatus for producing awell and determining the source of water being produced comprising astrainer having on its outer surface a substantially uniformdistribution of watersoluble radioactive material, means for producingthe well and means for examining the strainer for radioactive emanationsto determine the regions in which said radioactive material has beenremoved.

6. An apparatus for simultaneously producing a well and determining thesource of water being produced comprising a strainer initially having asubstantially uniform distribution of water-soluble radioactive materialthereon, means for restricting external axial flow of fluid, means forproducing the well and means for examining the strainer for radioactiveemanations to determine the regions in which said radioactive materialhas been removed.

7. An apparatus for simultaneously producing a well and determinin thesource of oil being produced comprising a strainer initially having asubstantially uniform distribution of oil-soluble radioactive materialthereon, means for producing the well and means for examining thestrainer REFERENCES CITED The following references are of record in thefile of this patent:

UNITED STATES PATENTS Number Name Date 2,352,993 Albertson July 4, 19442,358,945 Teichman Sept. 26, 1944

